The invention relates to a process for producing a metal melt by reducing metal-oxide-containing material, in particular iron-oxide-containing material, in a fluidized-bed reactor by the fluidized-bed method and by subsequently melting down the reduced material in a melt-down gasifier, in which there is generated from carbon-containing material a reducing gas which is used for reducing the metal-oxide-containing material by the fluidized-bed method, wherein both the reducing of the metal-oxide-containing material and the melting-down of the reduced material are effected under atmospheric excess pressure, as well as to a plant for carrying out the process.
A process of this kind is known for example from EP-A1-0 594 557 and WO 97/13880.
In order to permit a simple conveyance of the reduced material into the melt-down gasifier, the fluidized-bed reactors hitherto have been arranged at a level above a melt-down gasifier, and the reduced material from the fluidized-bed reactor has been charged into the melt-down gasifier via a conveying duct, utilizing gravitation. In plants of this kind, the conveying duct, which departs from the lower end area of the fluidized-bed reactor, runs into the upper area of the melt-down gasifier (WO 97/13880), which is designed as a dome-like gas settling space.
The charging of reduced material into the melt-down gasifier by aid of gravitational force does permit a simple charging operation but necessitates a considerable constructional height of the entire plant, given that the fluidized-bed reactors have to be arranged at a level above the melt-down gasifier. This results in relatively high investments not only for the plant itself, but also for a foundation work designed accordingly. Furthermore, a process of this kind has the disadvantage that only a single reactor line can be provided for a melt-down gasifier. This results from the spatial narrowness when arranging a reactor line above the melt-down gasifier.
From EP-A1-0 594 557 it is known to discharge reduced material from a fluidized-bed reactor by aid of discharge worms and to blow it, via sluices and by aid of a nitrogen injector, into the melt-down gasifier, namely in the area of the injecting levels for oxygen-containing gases. The sluices serve the purpose of balancing pressure differences between the fluidized-bed reactor and the melt-down gasifier.
The charging of reduced material into the melt-down gasifier by aid of a nitrogen injector does allow an arrangement of a fluidized-bed reactor at a lower level, i.e., not necessarily above the melt-down gasifier, but necessitates a relatively complex conveying means. Moreover, a process of this kind has the disadvantage that it is very difficult to charge the reduced material into the dome of the melt-down gasifier, given that the nitrogen injector causes major speeds of the reduced material at the site of introduction into the melt-down gasifier, which in turn runs counter to the function of the dome, which constitutes a gas settling space. Furthermore, the reduced material does not travel through the entire melt-down gasification zone but only through a portion of it.
The invention has as its object to further develop a process of the initially described kind so as to allow, on the one hand, for an arrangement of fluidized-bed reactors at a height level of the melt-down gasifier and, on the other hand, for a simple charging into the melt-down gasifier, in particular into its dome area, wherein neither the processes taking place in the melt-down gasifier are disturbed nor a large technical expenditure is necessary. It should be possible to charge the reduced material by utilizing gravitation.
In accordance with the invention, this task is accomplished for a process of the initially described kind by setting a lower pressure in an intermediate vessel situated above the meltdown gasifier than in the fluidized-bed reactor and by allowing the reduced material to flow, under relaxation, upwards from the fluidized-bed reactor into the intermediate vessel and conducting it from the intermediate vessel via a sluice system into the melt-down gasifier while it is pressurized, for the purpose of transferring the reduced material from at least one fluidized-bed reactor into the melt-down gasifier.
According to a preferred embodiment, the intermediate vessel is continuously filled with reduced material and continuously deaerated for reducing the excess pressure to roughly atmospheric pressure.
A preferred embodiment is characterized in that the reduced material located in the intermediate vessel is conducted, by gravitational conveyance, from the intermediate vessel into a bunker having approximately ambient pressure first, that after the bunker has been filled up with reduced material the intermediate vessel is flow-separated from the bunker, whereupon the bunker is set at least at the excess pressure given in the melt-down gasifier and the reduced material from the bunker is charged into the melt-down gasifier by gravitational force. It hereby becomes feasible to charge the reduced material without turbulences into the melt-down gasifier, preferably into its dome area, which is designed as a gas settling space.
A suitable variant is characterized in that a sluice, preferably in the form of a cellular wheel, is used for charging the reduced material from the bunker into the melt-down gasifier.
Another advantageous variant is characterized in that reduced material located in the intermediate vessel is conducted, by gravitational conveyance, from the intermediate vessel alternately into one of at least two bunkers having approximately ambient pressure first, that after one of the two bunkers has been filled up the intermediate vessel is flow-separated from the filled-up bunker, whereupon the filled-up bunker is set at least at the excess pressure given in the melt-down gasifier and the reduced material from the filled-up bunker is charged into the melt-down gasifier by gravitational force, and that during charging the reduced material into the melt-down gasifier the other bunker is filled with reduced material.
It is preferred to maintain an atmospheric excess pressure of 3 to 8 bars, preferably of 3 to 4 bars, in the melt-down gasifier.
A plant for producing a metal melt while using the process according to the invention, comprising a melt-down gasifier designed for atmospheric excess pressure, at least one fluidized-bed reactor designed for atmospheric excess pressure, a conveying means between the fluidized-bed reactor and the melt-down gasifier for conveying reduced material from the fluidized-bed reactor into the melt-down gasifier, and at least one gas connection duct between the melt-down gasifier and the fluidized-bed reactor for introducing reducing gas formed in the melt-down gasifier into the fluidized-bed reactor, is characterized in that the fluidized-bed reactor is arranged at roughly the height level of the melt-down gasifier, that the conveying means comprises a pipe which, departing from the fluidized-bed reactor, projects beyond the melt-down gasifier, that this pipe runs into an intermediate vessel having a deaerator, and that between the intermediate vessel and a fill hole provided in the dome of the melt-down gasifier for charging reduced material a sluice system is provided.
Here, the sluice system suitably is constituted by a bunker and a gastight discharge means between the bunker and the melt-down gasifier, wherein preferably the discharge means is constituted by a cellular-wheel means.
To permit a deaeration of the intermediate vessel and a pressure compensation of the bunker with the melt-down gasifier, preferably a shut-off device is provided, namely with regard to the flow, between the intermediate vessel and the bunker.
An advantageous embodiment is characterized in that a gas duct runs into the bunker to generate an excess pressure within the bunker, which gas duct is connected to a reducing-gas source or to an inert-gas source.
For the purpose of continuously charging reduced material, preferably the intermediate vessel is followed by at least two bunkers in parallel arrangement which may be flow-connected with the intermediate vessel via two connection ducts, respectively, provided with shut-off devices, respectively.
Suitably, the pipe is provided with a shut-off device, preferably closely adjacent to the fluidized-bed reactor.
The invention allows for the arrangement of several reactor lines running into a single melt-down gasifier, preferably with two or more fluidized-bed reactors being arranged next to the melt-down gasifier with regard to the level and each of the fluidized-bed reactors being flow-connected with the melt-down gasifier via an individual conveying means.